1. Field of the Invention
This application relates to transformers. More specifically, the invention relates to a breather for dehumidifying air drawn into an expansion tank in a transformer.
2. Related Art
Breathers for dehumidifying air entering an expansion vessel for an oil-filled transformer are conventional in the art. Such breathers include a moisture absorbing medium, i.e., a desiccant, that absorbs moisture from the incoming air. The medium can be regenerated, e.g., by heating, so that it can be reused after saturation.
As is known conventionally, it is important to have positive pressure in the transformer prior to regeneration of desiccant in a breather, so that the moisture pulled from the desiccant will be exhaled from the breather. Determining whether positive pressure exists has conventionally been done by measuring one or more of pressure, vacuum, flow or temperature.
Of the approaches, temperature-based monitoring is generally cheaper because temperature sensors are less expensive. Temperature monitoring to determine positive pressure generally includes taking successive temperature measurements at some time interval, typically hourly. A series of these measurements, generally on the order of days, can then be used to predict a positive pressure scenario that is optimal for regeneration. Such an approach is taken, for example, by U.S. Pat. No. 7,833,312.
A drawback of using the conventional temperature method, however, is that it relies upon the repeatability of the transformer loading cycle, which is not always certain.
Thus, there is a need in the art for a more reliable approach to determining timing and existence of positive pressure in a transformer.
There is also a need in the art for such an approach that is based on temperature measurements.